The goal of the proposed research is to understand how the many types of ion channels present in a single neuron work together to produce the firing patterns typical of that neuron. Ultimately, we would like to use this knowledge to develop ion channel-targeted pharmacological agents able to differentially regulate firing of different types of neurons and thereby treat pathophysiological behavior such as epilepsy. In previous grant periods, we focused on the functional roles of voltage-dependent calcium channels and sodium channels. The focus in the next grant period is to understand how different potassium channels combine to regulate the firing patterns of specific types of neurons. We will follow up preliminary data showing that inhibition of Kv2, Kv3, and BK potassium channels often causes paradoxical slowing rather than speeding of firing. We will test two possible mechanisms for this effect: enhanced inactivation of Na channels or recruitment of other potassium channels with slower deactivation. An important element of the approach is to compare action potentials in different types of neurons. We will focus on three types of neurons chosen to be examples of major electrophysiological phenotypes: hippocampal CA1 pyramidal neurons, cerebellar Purkinje neurons, and midbrain dopamine neurons. The experimental design will combine current clamp recordings of action potential firing with voltage- clamp analysis of the underlying currents, using both intact neurons in brain slice and acutely dissociated neurons, which allow fast voltage clamp to study gating on the rapid time scale of the action potential. A key feature o the approach will be to study both action potential firing and channel gating kinetics at 37C. Current clamp and voltage clamp experiments will be directly linked by the action potential clamp technique, in which recordings of natural firing behavior are used as voltage clamp commands to allow pharmacological dissection of the components of current generating patterns of action potentials. The research will include substantial characterization of pharmacological agents to block potassium channel subtypes.